In the steps of the photomechanical process in the field of duplication by printing, photographic images with continuous gradation are converted to halftone dot images wherein image density corresponds to the relative dot area, and are combined with originals of letters or line images to prepare printing originals.
In order to reproduce good line images and good halftone dot images, light-sensitive materials to be used for photomechanical process are required to provide enough high image contrast and enough high optical density to clearly discriminate image areas from non-image areas, or to show so-called superhigh contrast photographic properties (particularly 10 or more in gamma).
In recent years, photographic light-sensitive materials have been developed which can be handled in a bright room in spite of using silver halide as the light-sensitive element, thus meeting the demand for raising working efficiency by conducting a contact-exposure step (so-called contact work) using relatively low-speed light-sensitive materials in a brighter environment. The above-described demand can be met by a combination of a light-sensitive materials which has an extremely low sensitivity to visible light rays of 400 nm or longer in wavelength and a printer having a light source capable of emitting strong UV rays.
This type of silver halide photographic material which can be handled in a bright room have conventionally been prepared by adding inorganic desensitizing agents such as rhodium salts, iridium salts, cupric chloride, etc. upon formation of silver halide grains or by adding an organic desensitizing agent such as pinakryptol yellow, phenosafranine, etc. to an emulsion to thereby cause a substantial reduction in the intrinsic sensitivity of the silver halide emulsion to visible light rays (to the level of 1/10.sup.4 to 1/10.sup.5 of that of conventional emulsion).
On the other hand, in steps of the photomechanical process, it has been conventional to process a so-called lith type silver halide light-sensitive material comprising silver chlorobromide containing 40 mol% or less silver bromide with a hydroquinone developer (lith developer) having an extremely low effective concentration of sulfite ion (usually not more than 0.1 mol/liter) to obtain superhigh contrast photographic properties (particularly 10 or more in gamma).
In this process, however, the developer is extremely unstable against aerial oxidation due to the low sulfite concentration of the developer.
Therefore, there has been desired an image-forming system which solves the problem of unstable image formation in the above-described lith development and which provides superhigh contrast photographic properties when developed with a processing solution having good storage stability. U.S. Pat. Nos. 4,166,742, 4,168,977, 4,221,857, 4,224,401, 4,243,739, 4,272,606, 4,311,781, etc. have proposed a system of forming a superhigh contrast negative image of more than 10 in gamma, which comprises processing a surface latent image-forming silver halide photographic material containing a specific acylhydrazine derivative with a developer of 10.5 to 12.3 in pH containing 0.15 mol/liter or more of a sulfite preservative and having a good storage stability.
In the above-described novel image-forming system, superhigh contrast gradation can be obtained by utilizing electron injection reaction of the hydrazine derivative into silver halide. Japanese Patent Application (OPI) No. 238049/86 (the term "OPI" as used herein means a "published unexamined patent application") describes the technique of incorporating the hydrazine derivative in the above-described system to obtain a silver halide photographic material which provides high contrast gradation and which can be handled in a substantially bright room. However, this system provides still insufficient contrast to attain good image reproducibility.
The above-described technique enables one to obtain a silver halide photographic material which provides contrast gradation when processed with a stable developer and which can be handled in a bright room. However, the contrast thus obtained is still insufficient for obtaining good image reproducibility, and the contrast gradation properties obtained immediately after preparation of light-sensitive material changes with time when stored under the conditions of high temperature and high humidity due to poor storage stability.